1. Field of the Invention
The present invention relates to an infrared security sensor device of a kind equipped with a light projecting unit for projecting an infrared beam for object detection purpose, a light receiving unit for receiving the projected infrared beam and then outputting a detection signal, and an optical alignment unit for adjusting an optical axis between the light projecting unit and the light receiving unit.
2. Description of the Prior Art
The infrared security sensor device of an active type generally includes a light projecting unit having a light projecting element, a light receiving unit having a light receiving element and a sighting device and is so designed that when the light receiving unit receives an infrared beam projected from the light projecting unit, a detection signal is outputted to allow an object to be detected as light therebetween is intercepted, with a warning outputted subsequently. In this case, the sighting device is utilized to accomplish the adjustment of an optical axis between the light projecting unit and the light receiving unit and, while the sighting devices provided respectively in the light projecting unit and the light receiving unit are viewed, respective angles of a light projecting direction and a light receiving direction are manually adjusted to accomplish a rough adjustment of the optical axis with naked eyes. After this rough adjustment, the optical axis is finely adjusted so that the level of the detection signal may attain a value equal to or higher than a predetermined value.
In this type of the security sensor device, since because of a condition of use, including the axis-to-axis distance of the light projecting unit and the light receiving unit, and/or a change of environments around the site of installation such as, for example, a change in environment, the light receiving unit then receiving the light is unable to detect the interception of the infrared beam, there is the possibility that a failure to warn will occur during an alert time. By way of example, a situation, in which infrared rays of light impinged upon the light receiving unit, may be apt to occur because of a wraparound phenomenon, in which rays of light are projected from the light projecting unit and the infrared beam reflected by a wall surface or a ground surface between the light projecting unit and the light receiving unit impinges upon the light receiving. The degree of allowance required for a detecting unit keeps its alert status even though an environmental condition of the site of installation of the detecting unit gets worse is referred to as a sensitivity allowance. In general, the light receiving level (light receiving sensitivity), which is a signal level detected by the light receiving unit, is controlled by an AGC (Automatic Gain Control Circuit) of an amplifier on the side of the light receiving unit. In contrast thereto, as a security sensor device for controlling the light receiving sensitivity of the light receiving unit with a projected light power on the side of the light projecting unit in dependence of the above described site environment, an active type infrared security sensor device has been well known (such as disclosed in, for example, the patent document 1 listed below), in which when the light receiving unit saturates because of an excessive light projecting power, the light projecting power is lowered in a plurality of steps to allow the light receiving sensitivity of the light receiving unit to be automatically controlled. With a sensor for controlling on the side of the light projecting unit, the light intensity of the wraparound infrared beam or stray light can be lowered by controlling the light projecting power in the plurality of steps in a manner similar to the gain adjustment on the side of the standard light receiving unit. Also, because of the control to the optimum light projecting power, the amount of electricity consumed can be reduced and the durability can be increased by reducing the load on circuit component parts including elements of the light projecting unit.